This invention relates generally to systems and methods for determining the service life of air filters, and more particularly, for a system and method for calculating the service lives of filters for air purifying respirators.
Air purifying respirators (“APR”), including powered air purifying respirators (“PAPR”) rely on filters to remove chemical contaminants from the air flow through the respirator and into an operator's airway. Known filters prevent or impede the passage of one or more chemical contaminants from the atmosphere surrounding the respirator into the operator's airway through the filter. The filters may be used to filter the chemical contaminants for a limited time. For example, known filters prevent chemical contaminants from passing through the filters at concentrations above a breakthrough concentration for a service life of the filter. The breakthrough concentration may be an upper safety threshold for inhalation of the contaminants. For example, the operator of the respirator may not safely inhale a contaminant at concentrations above the breakthrough concentration without a significant increase in the risk of injury or illness from the contaminant. The service life of a filter may represent a predetermined time period that the filter may be exposed to the contaminants and prevent passage of the contaminants above the breakthrough concentration.
The service lives of filters may be affected by ambient conditions. For example, varying temperatures, barometric pressures, humidity, contaminant concentrations, breathing rates, chemical contaminants, and the like may significantly shorten the service lives of filters. If the shortened service life of a filter is not accurately tracked or measured, the operator of the respirator faces an increased risk of harm by using a filter after the filter's service life has expired. In order to monitor changes to the service lives of filters, a change out schedule may be provided that lists how often a filter needs to be replaced when used in certain environments or under certain types of ambient conditions. The service lives provided by the change out schedules are predetermined and may not account for changes to the service lives during use of the filters. For example, the change out schedules may not dynamically adjust the expected service life of a filter when the filter is used in an environment where the ambient conditions may shorten the service lives of the filter during use of the filter.
Another method for monitoring changes to the service lives of filters includes providing end of service life indicators (“ELSI”) on or with the filters. An ELSI includes a meter or other indication device that provides the operator of the respirator with a warning that the filter is about to expire. Known ELSIs may monitor concentrations of contaminants that are filtered by the respirator filters and, when the contaminant concentration increases above a threshold, an alarm is triggered to notify the operator that the filters need to be replaced. But, these known ELSIs suffer from many drawbacks, including the inability to factor in a variety of environmental factors into the determination of the end of the filter service life.
Thus, a need exists for a system and method for adaptively determining end of service lives for filters used in respirators based on the conditions under which the filters are used. The system and method should adapt the service life of the filter to the ambient conditions in which the filters are used to ensure that the operator of the respirator is provided sufficient time to replace the filter before the filter fails and permits unsafe levels of contaminants into the operator's airway.